2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1008 I TM Time 0 t di dt I TM 2 t 1 = Current 10% 50% t 1 V DM = Off-state voltage prior to switching Figure AN1008.4 Relationship of Maximum Current Rating to Time I 2 t Rating -- SCR and Triac The I 2 t rating gives an indication of the energy-absorbing capability of the Thyristor device during surge-overload conditions. The rating is the product of the square of the RMS current (I RMS ) 2 that flows through the device and the time during which the current is present and is expressed in A 2 s. This rating is given for fuse selection purposes. It is important that the I 2 t rating of the fuse is less than that of the Thyristor device. Without proper fuse or current limit, overload or surge current will permanently damage the device due to excessive junction heating. P G : Gate Power Dissipation -- SCR and Triac Gate power dissipation ratings define both the peak power (P GM ) forward or reverse and the average power (P G(AV) ) that may be applied to the gate. Damage to the gate can occur if these ratings are not observed. The width of the applied gate pulses must be considered in calculating the voltage and current allowed since the peak power allowed is a function of time. The peak power that results from a given signal source relies on the gate characteristics of the specific unit. The average power resulting from high peak powers must not exceed the average-power rating. T S , T J : Temperature Range -- SCR and Triac The maximum storage temperature (T S ) is greater than the maximum operating temperature (actually maximum junction temperature). Maximum storage temperature is restricted by material limits defined not so much by the silicon but by peripheral materials such as solders used on the chip/die and lead attachments as well as the encapsulating epoxy. The forward and off-state blocking capability of the device determines the maximum junction (T J ) temperature. Maximum blocking voltage and leakage current ratings are established at elevated temperatures near maximum junction temperature; therefore, operation in excess of these limits may result in unreliable operation of the Thyristor. AN1008.1) This value applies for open-gate or gate- resistance termination. Positive gate bias lowers the breakover voltage. Breakover is temperature sensitive and will occur at a higher voltage if the junction temperature is kept below maximum T J value. If SCRs and Triacs are turned on as a result of an excess of breakover voltage, instantaneous power dissipations may be produced that can damage the chip or die. I DRM : Peak Repetitive Off-state (Blocking) Current SCR I DRM is the maximum leakage current permitted through the SCR when the device is forward biased with rated positive voltage on the anode (DC or instantaneous) at rated junction temperature and with the gate open or gate resistance termination. A 1000 resistor connected between gate and cathode is required on all sensitive SCRs. Leakage current decreases with decreasing junction temperatures. Effects of the off-state leakage currents on the load and other circuitry must be considered for each circuit application. Leakage currents can usually be ignored in applications that control high power. Triac The description of peak off-state (blocking/leakage) current for the Triac is the same as for the SCR except that it applies with either positive or negative bias on main terminal 2.(Figure AN1008.2) I RRM : Peak Repetitive Reverse Current - SCR This characteristic is essentially the same as the peak forward off-state (blocking/leakage) current except negative voltage is applied to the anode (reverse biased). V TM : Peak On-State Voltage -- SCR and Triac The instantaneous on-state voltage (forward drop) is the principal voltage at a specified instantaneous current and case temperature when the Thyristor is in the conducting state. To prevent heating of the junction, this characteristic is measured with a short current pulse. The current pulse should be at least 100 s duration to ensure the device is in full conduction. The forward-drop characteristic determines the on-state dissipation. See Figure AN1008.5, Characteristics V BO : Instantaneous Breakover Voltage -- SCR and Triac Breakover voltage is the voltage at which a device turns on (switches to on state by voltage breakover). (Figure 15 and 25 A TO-220 T C = 25 C 40 A TO-218 0 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Positive or Negative Instantaneous On-state Voltage (v T ) - Volts 0 10 20 30 40 50 60 70 80 90 Positive or Negative Instantaneous On-state Current (i T ) - Amps Figure AN1008.5 On-state Current versus On-state Voltage (Typical) Explanation of Maximum Ratings and Characteristics for Thyristors (continued)